Attempting to precisely time sync data from two different cyclo-computers is problematic, they just never quite start and stop recording data at the same time, they all have quirks in how they deal with starting and stopping - some add an extra second or two (or three) of made up data while others trigger the "not pedalling" condition more quickly. Some have certain signatures in how they record certain data channels. The move to wireless ANT+ introduced a lot of such artefacts in the data recording process. It can be quite bad on some units, easily over inflating summation power data by several percent for certain types of rides (e.g. criteriums).

The old version of WKO, WKO+ had a feature that specifically allowed one to overlay data channel traces from more than one file but that feature doesn't exist in the same way in the new software.

Again, depending on what it is you are attempting to understand (it's not clear from your posts) there may be easier or more suitable methods.

One is simply to overlay the mean maximal power plot from each ride. That can highlight differences in at least the maximal reported values for all durations of the ride. While not covering all data - it does at least provide a first pass look at whether there are any obvious differences in peak values, and there often are, particularly at shorter duration end of the power duration curve. You can do this with appropriate software such as WKO4 or Golden Cheetah, although it's probably easier to export the chart data to Excel than attempt to get the software to overlay it.

Another example technique is plotting and overlaying the data using a virtual elevation method. This largely removes sync issues as it focuses on distance and calculated elevation - it's a great way to see at what point power files diverge from each other, since the method uses a cumulative process of calculating the energy balance for all the physics involved. It's quite a powerful diagnostic since it nails down where such divergences occur and that can help understand why it might be happening.

For those wondering, have a close look at how your meter manages data when you start/stop pedalling. Does it seem to have a repeated values when you stop? On which data channel? Does it treat power and cadence traces differently? For those with dual sided metering, what happens to your power balance data at those times? How is that affecting the summation figures for a ride?

When you start to look into this stuff, you realise there's a bit going on with the data and sometimes the various metrics can be misleading if not considered with due care.

i should of put this information in the first post.im wanting to compare a smart trainer power in this case a Neo with a Stages in a higher temperature environment (18 degrees - 28 degrees) over an hour long session.

figured out a rudimentary solution:Export each as a gpx format file, and then open them in excel.Pick the time scale from 1, and the power data from both and paste onto 1 sheet.Make simple xls line chart.

tomee wrote:great info Alex, thank you for taking the time to write that up.

i should of put this information in the first post.im wanting to compare a smart trainer power in this case a Neo with a Stages in a higher temperature environment (18 degrees - 28 degrees) over an hour long session.

figured out a rudimentary solution:Export each as a gpx format file, and then open them in excel.Pick the time scale from 1, and the power data from both and paste onto 1 sheet.Make simple xls line chart.

Post your results, be interested to see what you find.

It would not surprise me to see some divergence.

The problem then becomes understanding the cause of the difference, which in the case of the set up you mention could be due to either of or both of technical and biological factors.

Alex Simmons/RST wrote:It would seem the primary differences are at low power and at high power.

yeah and im seeing the same pattern on all my other rides regardless of temperature. neo reading lower during low wattage and slightly higher in the higher ranges

not sure whether its to do with drive train losses etc

There are a range of possible reasons for the variability in reported power, as well as a difference.

Given one of the devices is a unilateral Stages, there is every chance that your power output is asymmetric across the power range and this is being reflected in Stages data, which assumes perfect symmetry at all times and in all conditions and scenarios. We know this is never the case, everybody has some level of asymmetry and variable asymmetry is also normal.

Of course there is nothing to suggest to Neo is spot on either (other than their marketing claims), some have reported it varies for them depending on cadence, and I doubt it has been subjected to testing of scientific rigour.

Drivetrain losses can account for 1-3% of total power as well, so devices at crank/pedals should read higher than those measuring at the cog/hub/wheel/tyre.

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